The present invention relates to the design and fabrication of semiconductor power devices, more particularly to robust power devices. For example, diodes that are not sensitive to High Temperature Reverse Bias (HTRB) and Humidity test conditions.
Reliability is the characteristic expressed by the probability that a given device will perform its intended function for a specific period of time under user defined conditions. The reliability of a new product is tested by having the product undergo one or more tests that are conducted under harsh conditions to obtain reliability results after a short test period. Such tests are generally conducted under “extreme” conditions to achieve an acceleration effect. High Temperature Reverse Bias (HTRB) and Humidity tests are two such tests.
HTRB test checks the ability of the samples to withstand a reverse bias while being subjected to the maximum ambient temperature that the parts are rated to withstand. Humidity test checks the ability of the package and passivation layers to resist moisture penetration. The sample is loaded into an environmental chamber. The relative humidity is then increased to 85%, and the temperature is elevated.
It is well known that in semiconductor devices early failures occur when a part with some latent defect passes screening but later deteriorates and prematurely fails in the end application. The cause of the failure might be from poor design, inconsistent process control, failure in passivation, die microcracks, junction contamination, die bonding anomalies and so forth. Furthermore devices used in high power electronic equipment are exposed to different temperature and humidity conditions.
The passivation of the surface of discrete power devices determines the ability of the device to withstand high surface electric fields. The surface charge induced by the passivation layer strongly influences the electric fields in the bulk. Generally silicon dioxide and silicon nitride sandwich or semi-insulating polycrystalline silicon or zinc borosilicate glass or oxide and metal field plate sandwich are used as a passivation layer. It has been observed that depending upon the design of passivation layers devices are sensitive to reliability testing, i.e., increase in leakage current during HTRB and Humidity test conditions. Consequently, among other needs, it would be desirable to make a robust power device that can withstand HTRB and Humidity test conditions.